Lithium ion secondary battery system, and method for operating lithium ion secondary battery

ABSTRACT

A drop of discharge or charge capacity in discharging or charging with a large current is reduced without changing a design of a lithium ion secondary battery itself. When the lithium ion secondary battery for a car or a vehicles such as an electric automobile and a hybrid automobile is discharged or charged with, for instance, a large current not less than 5C, an intermittent power feeding of repeatedly executing a power feeding (t 2 ) and a pause (t 1 ) is carried out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium ion secondary battery systemand a method for operating the lithium ion secondary battery system.

2. Description of the Prior Art

In recent years, with growing environmental problem concerns,developments of an electric automobile or a hybrid automobile areactively carried out. Accompanied with this, developments of a mediumpower battery of about 100 W to 1000 W used for the electric automobileor the hybrid automobile or the like, or a high power battery to be notless than 1000 W are advanced. As a battery for the automobile, althougha large-sized battery by combining a large amount of the lead-acidbatteries or the nickel-hydrogen batteries is mainly utilized, suchbattery has the problem that energy density per weight is low, andenergy density per volume is low. For that reason, it is desired thatthe lithium ion secondly battery, which shows more excellentcharacteristics in an output or a heating or the like, may be made toapply to such automobile.

Conventionally, in the lithium ion secondary battery using the metalliclithium for a negative electrode, when carrying out quickly charging,lithium is extracted as dendrite to be crystalline state of acicularand/or dendritic, with the result that there is the problem of bringingabout short circuit between the positive electrode and the negativeelectrode. In order to solve such the problem, there is disclosed thetechnique capable of repeatedly charging without producing chargingfailure while preventing growth of dendrite, upon charging with pulsecurrent manner of repeatedly executing power feeding and pausing (PatentLiterature 1).

On the other hand, in order to solve such the problem caused by thedendrite growth, the lithium secondary battery, which uses carbonmaterial for a negative electrode, has been developed. However, in sucha lithium ion secondary battery, there is the problem of occurringcapacity loss at an initial charging caused by irreversibility of thecarbon material. In order to solve such the problem, there is discloseda technique to improve battery capacity, upon causing the battery toovercharge with small current at the time of initial charging (PatentLiterature 2).

Further, conventionally, even though when the charge-discharge currentof the lithium type rechargeable battery is small, in order to preventdisappearance of a passivation film formed in the vicinity of a lithiumpositive electrode, there is disclosed a technique, which intermittentlyuses the current (for instance, not less than C/2, when nominal capacityof the battery is taken to as C) larger than necessary charge-dischargecurrent (Patent Literature 3).

-   Patent Literature 1: Japanese Laid-Open Patent Publication No.    H06-36803-   Patent Literature 2: Japanese Patent No. 2949705-   Patent Literature 3: Japanese Laid-Open Patent Publication No.    S64-77432-   Patent Literature 4: Japanese Laid-Open Patent Publication No.    2002-260673 (TABLE 3, Comparison example 3)

SUMMARY OF THE INVENTION

Meanwhile, at present, the capacity of the lithium ion secondary batteryis at most to be degree of 130 mAh/g, even though some devices are madeto apply to electrode material. However, in cases where the lithium ionsecondary battery is made to apply to cars or vehicles such asautomobiles or motorcycles or the like, the cars necessitate chargingand discharging with a large current not less than 10 A at the time ofacceleration or at the time of deceleration. In order to obtain largecurrent without changing design of the lithium ion secondary batteryitself, for instance, it is conceivable that the lithium ion secondarybattery is made to charge and discharge with high current value withrespect to its nominal capacity. However, in the conventional lithiumion secondary battery, there is the problem that dischargeable realcapacity becomes small with increasing current value to the nominalcapacity of the battery. For instance, as shown in the JapaneseLaid-Open Patent Publication No. 2002-260673, in the conventionallithium ion secondary battery, when discharge rate is taken to as 3 C,the discharge capacity is substantially lowered. When current value ismade to increase and continuous power feeding time is made to lengthen,influence of diffusion resistance of the lithium ion becomes large, withthe result that moving speed of the lithium ion decreases. Therefore,the IR drop increases such that the voltage exceeds an upper limitvoltage of the battery (an open circuit voltage) or a lower limitvoltage (an end-of-discharge voltage) to cause the above problem.

The object of the present invention is to provide a technique to reducea drop of discharge or charge capacity in discharging or charging with alarge current without changing the design of a lithium ion secondarybattery itself.

According to the present invention, there is provided a method foroperating a lithium ion secondary battery system comprising: carryingout an intermittent power feeding in which a power feeding and a pauseare repeatedly executed, when a lithium ion secondary battery isdischarged or charged with not less than a predetermined discharge rateor charge rate.

Here, it is also possible to judge whether or not the discharge rate orthe charge rate is not less than the predetermined discharge rate or thecharge rate based on the current value. The lithium ion secondarybattery of the present invention is capable of being applied to anapparatus such as an automobile or the like, which requires thedischarging or the charging with a large current. According to thepresent invention, even though when the lithium ion secondary battery isdischarged or charged with a large current, an intermittent powerfeeding is carried out, therefore, it is possible to reduce influence ofdiffusion resistance of the lithium ion, and to diffuse the lithium ionuniformly. As a result, the movement of the lithium ion is enhanced,therefore, it is possible to suppress decrease of an effective capacityof the lithium ion secondary battery. Owing to this, it is possible tosuitably carrying out the discharging or the charging with a largecurrent without changing the design of the lithium ion secondarybattery.

In the present invention, it is possible to carry out such theintermittent power feeding at the time of normal operation of thelithium ion secondary battery. Here, the time of normal operation meansthe time when charging or discharging to a load or a battery charger isactually executed, not limited to an initial charging.

In the method for operating the lithium ion secondary battery system ofthe present invention, the pause may be executed for a period not lessthan the period required for the voltage of the lithium ion secondarybattery to restore not less than 70% of the open circuit voltage afterthe lithium ion secondary battery is discharged until the voltagethereof reaches the discharge end voltage, when the lithium ionsecondary battery is discharged.

Although a lower limit of the pausing time is not particularly limited,after discharging the lithium ion secondary battery until the voltagethereof reaches the end voltage, the pause can be executed during thetime period required for the voltage to restore up to not less than 70%of the open circuit voltage. By executing the pause for such the period,the state of the lithium ion becomes a homogeneous equilibrium from aheterogeneous state, therefore, it is possible to suppress decrease ofeffective capacity of the lithium ion secondary battery. As will bedescribed later, with referring to FIG. 3, when stopping the powerfeeding, after carrying out the discharging, voltage is restoredquickly. The pausing period can be set to, for instance, not less than0.001 sec. Further, although an upper limit of the pausing time is notparticularly limited, the upper limit of the pausing time can be set toa period at which influences on operation of an apparatus, which ismounted with the lithium ion secondary battery do not occur, forinstance, not more than 10 sec. Owing to this, it is possible toincrease substantially effective capacity without affecting on operationof the apparatus.

In the method for operating the lithium ion secondary battery system ofthe present invention, said pause may be executed for a period not lessthan the period required for the voltage of the lithium ion secondarybattery to go down by not less than 70% of a voltage difference betweenthe open circuit voltage and the charge end voltage after the lithiumsecondary battery is charged until the voltage thereof reaches thecharge end voltage, when the lithium ion secondary battery is charged.

Here, the charge end voltage is an end voltage where the lithium ionsecondary battery is charged. When the lithium ion secondary battery ischarged with a large current, movement of the lithium ion is inhibitedbecause of influence of diffusion resistance of the lithium ion, sothat, the charge end voltage becomes not less than the open circuitvoltage. Also in such a case, by stopping power feeding, the state oflithium ion is changed to a homogeneous equilibrium from a heterogeneousstate, therefore, it is possible to have the voltage of the lithium ionsecondary battery near to the open circuit voltage.

In the method for operating the lithium ion secondary battery system ofthe present invention, it is possible to execute the power feeding andthe pause repeatedly with constant time intervals.

In the method for the lithium ion secondary battery system of thepresent invention, said intermittent power feeding may be carried outwhen the discharge rate or the charge rate is not less than 5 C.

Here, a charge (discharge) rate for having the lithium ion secondarybattery in a fully charged state into a perfectly discharged state inone hour is assumed to be 1 C. When the lithium ion secondary battery isdischarged or charged with a large current, the above describedinfluence of the diffusion resistance of the lithium ion can be aproblem, however, according to the present invention, since aheterogeneous state of lithium ions can be eliminated by executing theintermittent power feeding, the decrease of effective capacity of thelithium ion secondary battery can be restrained, thus, it is possible tosuppress decrease of the effective capacity of the lithium ion secondarybattery.

In the method for operating the lithium ion secondary battery system ofthe present invention, the lithium ion secondary battery may include apositive active material having an average discharge potential to thelithium metal of not less than 4.5V. Further, in the method for thelithium ion secondary battery system of the present invention, thelithium ion secondary battery may include a positive active materialconstituted with a 4V class or a 5V class of a spinel type lithiummanganese composite oxide. Further, the lithium ion secondary batterymay include a negative active material constituted by a carbon materialsuch as natural graphite, artificial graphite or the like as the mainingredient.

In the method for operating the lithium ion secondary battery system ofthe present invention, the lithium ion secondary battery may beincorporated in a power supply device of an electric automobile or ahybrid automobile.

According to the present invention, there is provided a lithium ionsecondary battery system comprising: a lithium ion secondary battery;and a control unit which carries out an intermittent power feeding inwhich a power feeding and a pause are repeatedly executed, when alithium ion secondary battery is discharged or charged with not lessthan a predetermined discharge rate or charge rate.

In the lithium ion secondary battery system of the present invention,said control unit may execute said pause for a period not less than theperiod required for the voltage of the lithium ion secondary battery torestore up to not less than 70% of the open circuit voltage after thelithium ion secondary battery is discharged until the voltage thereofreaches the discharge end voltage, when the lithium ion secondarybattery is discharged.

The lithium ion secondary battery system of the present invention mayfurther comprise a voltage measuring unit which measures a voltage ofthe lithium ion secondary battery, wherein said control unit may executesaid pause for a period not less than the period required for thevoltage of the lithium ion secondary battery to go down by not less than70% of a voltage difference between the open circuit voltage and thecharge end voltage after the lithium secondary battery is charged untilthe voltage thereof reaches the charge end voltage, when the lithium ionsecondary battery is charged.

The lithium ion secondary battery system of the present invention mayfurther comprise a detection unit which detects the discharge rate orthe charge rate of the lithium ion secondary battery, wherein saidcontrol unit may carry out said intermittent power feeding when thedischarge rate or the charge rate of the lithium ion secondary batteryis not less than 5 C.

In the lithium ion secondary battery system of the present invention,the lithium ion secondary battery may include a positive active materialhaving an average discharge potential to the lithium metal of not lessthan 4.5V. Further, in the lithium ion secondary battery system of thepresent invention, the lithium ion secondary battery may include apositive active material constituted with a 4V class or a 5V class of aspinel type lithium manganese composite oxide. Further, the lithium ionsecondary battery may include a negative active material constitutedwith a carbon material such as natural graphite, artificial graphite orthe like as the main ingredient.

In the lithium ion secondary battery system of the present invention,the lithium ion secondary battery may be incorporated in a power supplydevice of an electric automobile or a hybrid automobile.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages will be moreapparent from the following preferred embodiment and the accompanyingdrawings.

FIG. 1 is a block diagram showing an example of a lithium ion secondarybattery system of the present invention.

FIG. 2 is a view showing a current pattern controlled by a control unit.

FIG. 3 is a view showing a recovery state of the voltage, afterdischarging the lithium ion secondary battery.

FIG. 4 is a view showing a current pattern controlled with the controlunit.

DETAILED DESCRIPTION OF THE INVENTION

The lithium ion secondary battery described in the following embodimentis capable of being used in such a way as to be appropriatelyincorporated in a power supply device for an apparatus requiringrelatively large current, such as an electric automobile or a hybridautomobile or the like.

The secondary battery of the present invention has a positive electrodewith lithium containing metal composite oxide as a positive activematerial and a negative electrode having a negative active materialcapable of occluding and releasing lithium. There is provided aseparator between the above positive electrode and negative electrode soas not to form an electrical contact therebetween. Further, the abovepositive electrode and the negative electrode are in a state where bothare dipped in the electrolyte having lithium ion conductivity, and theseare in a state where the electrodes in the electrolyte are sealed in abattery case. A secondary battery system of the present invention is abattery pack in which a plurality of the secondary batteries constitutedas above are connected in series.

In the secondary battery of the present embodiment, a positive electrodematerial of 4V class or a positive electrode material of 5V class(material having the average discharge potential not less than 4.5V tothe lithium metal) is used as the positive active material.

As for the positive electrode material of 4V class, it is possible touse lithium containing metal oxides, such as, for instance, LiCoO₂,LiNiO₂, LiMn₂O₄ or the like. Among them, a spinel type lithium-manganesecomposite oxide represented by LiMn₂O₄ is preferably used. In caseswhere LiMn₂O₄ is used, it is also possible to replace trivalent Mn withanother element. For instance, it is possible to use a lithium-manganesecomposite oxide represented by a composition formula LiM_(x)Mn_(2-x)O₄(M expresses not less than one kind selected from Al, B, Cr, Co, Ni, Ti,Fe, Mg, Ba, Zn, Ge, and Nb, 0.01=x=1). Because of this, it is possibleto improve structural stability.

As for the positive electrode material of 5V class, lithium containingcomposite oxide is suitably used, for instance. As for the lithiumcontaining composite oxide, the spinel type lithium-manganese compositeoxide represented by LiMn_(1-x)M_(x)O₄ (0=x<1, M=Ni, Co, Cr, Cu, or Fe),olivine type lithium containing composite oxide represented by LiMPO₄(M=Co, Ni or Fe), and inverse spinel type lithium containing compositeoxide such as LiNiVO₄ or the like are exemplified.

Among the above positive active materials, it is preferable to useLiNi_(x)Mn_(2-x)O₄ which is a spinel type lithium-manganese compositeoxide having a stable crystal structure, and from which high capacity ofnot less than 130 mAh/g is obtained. A composition ratio x of Ni in thisactive material is set to a range of 0.4 to 0.6. In such a way as above,it is possible to improve energy density, while sufficiently ensuringdischarge region at not less than 4.5V.

Further, as for the positive active material, a material in which a partof Mn in LiNi_(x)Mn_(2-x)O₄ is made to replace with Li, Al, Mg, Ti, Sior Ge is used, so that the cycle characteristic is further improved.Upon replacing a part of Mn with the above element, the crystalstructure of the active material is further stabilized. For this reason,since decomposition of electrolyte is suppressed, generated amount ofdecomposition product of electrolyte decreases. Consequently, it isestimated that deposition of the decomposition product of theelectrolyte to the negative electrode is reduced.

Further, in the active material obtained in such a way that a part of Owithin the above active material is made to replace with F or Cl or thelike, crystal structure is still further stabilized, so that morepreferable cycle characteristics is obtained. In addition, in a systemwhere a part of Mn is replaced with monovalent to trivalent elementssuch as Li, Al, and Mg, as the Ni valence is increased, the capacity islowered as the displacement amount increases. Replacement of oxygen withhalogen such as fluorine, and chlorine cancels the increase of Nivalence, therefore, it has an additional merit to keep high capacity.

As for the negative active material, although it is possible to usevarious carbon materials such as natural graphite, artificial graphiteor the like as a main ingredient, among them, it is preferable thatamorphous carbon is taken to as a main ingredient. In such a way asabove, it is possible to reduce deposition of the decomposition productof the electrolyte on the surface of the negative electrode, so that itis possible to contribute to cycle characteristic improvement. Here, theamorphous carbon in the present invention is the carbon material with abroad scattering band having a peak within a range of 15 to 40 degree ina 2θ value of X-ray diffraction method using CuK a ray.

In addition, it may be suitable that the negative active materialcontains material capable of occluding and releasing lithium as anaccessory ingredient. As for the material capable of occluding andreleasing lithium, it is possible to use the mixture of carbon material,Li metal, Si, Sn, Al, SiO, SnO, or the like.

The negative active material is formed on a current collector with aconductive agent and a binder. As for the conductive agent, it ispossible to use powders of conductive oxide in addition to the carbonmaterial. As for the binder, poly-vinilydene fluoride can be used. Asfor the current collector, a metallic thin film with Cu as a mainconstituent can be used.

Next, there will be described operation of the lithium ion secondarybattery of the present invention. By applying voltage to the positiveelectrode and to the negative electrode, the lithium ion emits from thepositive active material, and the lithium ion is occluded in thenegative active material, with the result the battery becomes a chargedstate. On the other hand, contrary to the charging time, when thepositive electrode is brought into electrical contact with the negativeelectrode at an outer part of the battery, lithium ions are emitted fromthe negative active material and lithium ions are occluded in thepositive active material, so that electrical discharge takes place.

There is no limitation in the shape of the battery of the presentinvention, accordingly, the positive electrode and the negativeelectrode, which are faced with each other while putting a separatortherebetween, are capable of adopting a form such as a winding type, alaminating type or the like, so that it is possible to use a coin type,a laminate pack, a square type cell, and a tubular type cell as being acell.

FIG. 1 shows an example of the lithium ion secondary battery system inthe embodiment of the present invention. The lithium ion secondarybattery system 10 includes a lithium ion secondary battery 12, a controlunit 14, a load (or a battery charger) 16, a current sensor 18 and avoltage sensor 20. The control unit 14 controls power feeding to theload (or the battery charger) 16 when the lithium ion secondary battery12 is discharged or charged. The current sensor 18 measures a currentvalue of the lithium ion secondary battery 12. The voltage sensor 20measures a voltage of the lithium ion secondary battery 12. The controlunit 14 carries out an intermittent power feeding to the load (or thebattery charger) 16 in the case where a current value, which is measuredby the current sensor 18, is not less than a predetermined value. Ameans, by which the control unit 14 carries out the intermittent powerfeeding, is not particularly limited. It is possible to provide a knownswitch circuit or the like to carry out the power feeding to the load(or the battery charger) 16 when the current value is not less than apredetermined value. In addition, the control unit 14 may calculate thedischarge rate or the charge rate of the lithium ion secondary battery12 based on the current value measured by the current sensor 18; and maycarry out the intermittent power feeding to the load (or the batterycharger) 16, when the discharge rate or the charge rate is not less thana predetermined value.

FIG. 2 shows an intermittent current pattern controlled by the controlunit 14. In such a way as above, the control unit 14 controls thelithium ion battery 12 to carry out the discharge or the charge whilerepeatedly executing a power feeding of a predetermined time t₂ and apause of a predetermined time t₁.

FIG. 3( a) is a view showing a recovery state of the voltage when thedischarge is made with the discharge rate of 20C until the voltagereaches the end voltage (2.5V) and then terminated. FIG. 3( a) shows arate of recovery (%), and FIG. 3( b) shows a recovery voltage value (V).As shown, at the time after approximately 0.001 sec after thetermination, the voltage is restored up to not less than approximately70% of the open circuit voltage (4.1V). Here, although the recoverystate of the voltage when the discharge is made with the discharge rateof 20 C is shown, the similar recovery state is shown when the dischargeis made with the discharge rate of 5 C or 10 C. Although the pause timeis not particularly limited, it is possible to be, for instance, notless than 0.001 sec to not more than 10 sec.

Also, when charging the lithium ion secondary battery 12 (see FIG. 1),the pause time is not particularly limited, and it is possible to setthe pause time to the same degree of time as the pause time of thedischarging time. In addition, at the charging time, the control unit 14may refer to the voltage of the lithium ion secondary battery 12measured by the voltage sensor 20 and terminate the power feeding untilthe voltage becomes value not more than the open circuit voltage whenthe voltage is larger than the open circuit voltage of the lithium ionsecondary battery 12.

Although FIG. 2 shows an example where the discharge is carried out withthe current value (the discharge rate or the charge rate) set to aconstant value, the control unit 14 may carry out the intermittentdischarge when the current value is varied as shown in FIG. 4.

EMBODIMENT EXAMPLE Embodiment Example 1

Here, the lithium ion secondary battery was manufactured with positiveelectrode materials of 4V class.

First, the negative electrode body was formed in such a way as to applyamorphous carbons to both faces of a copper foil sheet (thicknessapproximately 15 μm) with a thickness of approximately 50 μm while usingthe amorphous carbon as the negative active material. It should be notedthat, as for the amorphous carbon, Carbotron P (registered trademark)produced by KUREHA CHEMICAL INDUSTRY CO. LTD was used. As for thepositive active material, lithium-manganese composite oxides were used;and the positive electrode body was formed in such a way as to apply thelithium-manganese composite oxides to both faces of an aluminum foilsheet (thickness approximately 20 μm) with a thickness of approximately70 μm. Next, the negative electrode body and the positive electrode bodywere placed to face each other in such a way that there was noelectrical contact between the negative electrode body and the positiveelectrode body, with a laminated type separator (thickness approximately25 μm) of a polyethylene film and a polypropylene film placedtherebetween. After that, a nickel negative electrode terminal(thickness approximately 100 μm) and an aluminum positive electrodeterminal (thickness approximately 100 μm) were attached to the electrodecurrent collectors (uncoated part) of the negative electrode body andthe positive electrode body respectively by ultrasonic welding.Successively, the above formed structure was wrapped with a laminatedfilm (thickness approximately 100 μm) of an aluminum foil, and anelectrolyte, which was prepared by dissolving lithium phosphatehexafluoride in nonaqueous solvent of propylene carbonate and methylethyl carbonate, was injected therein. Then, the structure was thermallyfused and sealed under a reduced pressure resulting in a lithium ionsecondary battery.

With the lithium ion secondary battery (nominal capacity 2 Ah) preparedas above, the intermittent discharging (repeated execution of 10 secdischarging and 0.8 sec pause) was carried out with the discharge rateas shown in below TABLE 1, and the discharge period up to the endvoltage (2.5V) was measured to calculate the effective capacity in eachcase. The result thereof is shown in TABLE 1. In addition, in eachdischarge rate, similarly, the effective capacity was calculated in thecase when the discharging was carried out continuously. In TABLE 1, theeffective capacity magnification which was obtained by dividing theeffective capacity of the intermittently discharge by the effectivecapacity of the continuous discharge is also shown.

TABLE 1 EFFECTIVE EFFECTIVE CAPACITY CAPACITY OF OF DIS- INTERMITTENTCONTINUOUS EFFECTIVE CHARGE DISCHARGE DISCHARGE CAPACITY RATE (Ah) (Ah)MAGNIFICATION  1 C 1.72 1.70 1.01  5 C 1.69 1.59 1.06 10 C 1.55 1.201.29 20 C 0.98 0.29 3.38

As shown in TABLE 1, the effective capacity magnification, when thedischarge rate is 1 C, is approximately 1.01, and there is littledifference in the effective capacities of the intermittent discharge andthe continuous discharge. However, it is shown that the effectivecapacity magnification increases as the discharge rate increases, bycarrying out the intermittent discharge. Thus, according to the methodfor operating the lithium ion secondary battery system of the presentinvention, in particular, when the discharge rate is high, it ispossible to improve the energy density per weight and the energy densityper volume of the lithium ion secondary battery.

Embodiment Example 2

Similar to the embodiment example 1, the lithium ion secondary batterywas manufactured. With the lithium ion secondary battery, theintermittent discharging (repeated execution of 1 sec discharging and 1sec pause) and the continuous discharging were carried out, with thedischarge rate of 25 C, and the dischargeable periods until the voltagereached the end voltage (2.5V) were measured. Then, the effectivecapacity in each case was calculated. The result thereof is shown inTABLE 2. In TABLE 2, the effective capacity magnification obtained bydividing the effective capacity of the intermittent discharge by theeffective capacity of the continuous discharge is also shown.

TABLE 2 EFFECTIVE EFFECTIVE CAPACITY CAPACITY OF OF DIS- INTERMITTENTCONTINUOUS EFFECTIVE CHARGE DISCHARGE DISCHARGE CAPACITY RATE (Ah) (Ah)MAGNIFICATION 25 C 0.64 0.28 2.30

As shown above, it is shown that the effective capacity magnificationincreases by carrying out the intermittent discharging in the case wherethe discharge rate is set to 25 C. Thus, even though in the case wherethe discharge rate is high, it has been possible to reduce lowering ofthe effective capacity, by carrying out intermittent discharging, aswell.

Embodiment Example 3

Here, a lithium ion secondary battery was manufactured with positiveelectrode materials of 5V class. The lithium ion secondary battery wasobtained with the same producing method as the embodiment example 1,other than using LiNi_(0.5)Mn_(1.5)O₄ as the positive active material.With the lithium ion secondary battery manufactured as above, theintermittent discharging (repeated execution of 10 sec discharging and0.8 sec pause), and the continuous discharging, both with the dischargerate of 20 C, were carried out, and the discharge periods until thevoltage reached the end voltage (2.5V) were measured. Then, theeffective capacity in each case was calculated. The result thereof isshown in TABLE 3. TABLE 3 also shows effective capacity magnificationobtained by dividing the effective capacity of the intermittentdischarge by the effective capacity of the continuous discharge.

TABLE 3 EFFECTIVE EFFECTIVE CAPACITY CAPACITY OF OF DIS- INTERMITTENTCONTINUOUS EFFECTIVE CHARGE DISCHARGE DISCHARGE CAPACITY RATE (Ah) (Ah)MAGNIFICATION 20 C 0.80 0.23 3.48As shown in TABLE 3, it has been indicated that the effective capacityincreases by carrying out the intermittent discharging in cases wherethe positive electrode material of 5V class is used when the dischargerate is high, as well.

Embodiment Example 4

Similar to the embodiment example 1, the lithium ion secondary batterywas manufactured and the intermittent charging (repeated execution of 10sec charging and 0.8 sec pause), and the continuous charging, both withthe charge rate of 20 C, were carried out. The lithium ion secondarybatteries charged as above were made to respectively dischargecontinuously with 1 C, and the discharge periods until the voltagereached the end voltage (2.5V) were measured.

Then, the effective capacity in each case was calculated. It has beenshown in this case as well that the effective capacity increases morewhen the intermittent charging was carried out than when the continuouscharging was carried out.

As above, there is described the present invention based on theembodiment and the embodiment example. This embodiment and embodimentexample are only illustrations, consequently, various modified examplesof the respective components or combinations of respective treatmentprocesses are possible, also those modified examples fall within thescope of the present invention that is understood by person skilled inthe art.

For instance, although it is described in the above embodiment example,that the intermittent discharge or charge is carried out with a patternhaving a constant power feeding periods and pause periods, respectively,the pause period or the power feeding period may be respectively set todifferent time intervals.

As described above, according to the present invention, it is possibleto reduce drop of the discharge or charge capacity when discharging orcharging the lithium ion secondary battery with a large current, withoutchanging design of the lithium ion secondary battery itself. Owing tothis, since the effective capacity of the battery increases, it ispossible to reduce amount of battery mounting, so that it is possible toexpect weight reduction of a system, and cost reduction.

1. A method for operating a lithium ion secondary battery systemcomprising: carrying out an intermittent power feeding in which a powerfeeding and a pause are repeatedly executed, when a lithium ionsecondary battery is discharged with not less than a predetermineddischarge rate to a discharge end voltage, wherein said pause isexecuted for a period not less than the period required for the voltageof the lithium ion secondary battery to restore up to not less than 70%of an open circuit voltage after the lithium ion secondary battery isdischarged until the voltage thereof reaches the discharge end voltage,when the lithium ion secondary battery is discharged.
 2. The method foroperating the lithium ion secondary battery system as set forth in claim1, wherein an intermittent power feeding in which a power feeding and apause are repeatedly executed, when a lithium ion secondary battery ischarged with not less than a predetermined charge rate, wherein saidpause is executed for a period not less than the period required for thevoltage of the lithium ion secondary battery to go down by not less than70% of a voltage difference between the open circuit voltage and thecharge end voltage after the lithium secondary battery is charged untilthe voltage thereof reaches the charge end voltage, when the lithium ionsecondary battery is charged.
 3. The method for operating the lithiumion secondary battery system as set forth in claim 1, wherein saidintermittent power feeding is carried out when the discharge rate is notless than 5 C.
 4. The method for operating the lithium ion secondarybattery system as set forth in claim 1, wherein the lithium ionsecondary battery includes a positive active material having an averagedischarge potential to the lithium metal of not less than 4.5V.
 5. Themethod for operating the lithium ion secondary battery system as setforth in claim 1, wherein the lithium ion secondary battery isincorporated in a power supply device of an electric automobile or ahybrid automobile.
 6. The method for operating the lithium ion secondarybattery as set forth in claim 1, wherein an intermittent power feedingin which a power feeding and a pause are repeatedly executed, when alithium ion secondary battery is charged with not less than apredetermined charge rate.
 7. The method for operating the lithium ionsecondary battery as set forth in claim 6, wherein said intermittentpower feeding is carried out when the charge rate is not less than 5 C.8. A lithium ion secondary battery system comprising: a lithium ionsecondary battery; and a control unit which carries out an intermittentpower feeding in which a power feeding and a pause are repeatedlyexecuted, when a lithium ion secondary battery is discharged with notless than a predetermined discharge rate to a discharge end voltage, andwherein said control unit executes said pause for a period not less thanthe period required for the voltage of the lithium ion secondary batteryto restore up to not less than 70% of an open circuit voltage.
 9. Thelithium ion secondary battery system as set forth in claim 8, whereinsaid control unit executes said pause after the lithium ion secondarybattery is discharged until the voltage thereof reaches the dischargeend voltage, when the lithium ion secondary battery is discharged. 10.The lithium ion secondary battery system as set forth in claim 8,further comprising a voltage measuring unit which measures a voltage ofthe lithium ion secondary battery, wherein an intermittent power feedingin which a power feeding and a pause are repeatedly executed, when alithium ion secondary battery is charged with not less than apredetermined charge rate, wherein said control unit executes said pausefor a period not less than the period required for the voltage of thelithium ion secondary battery go down by not less than 70% of a voltagedifference between the open circuit voltage and the charge end voltageafter the lithium secondary battery is charged until the voltage thereofreaches the charge end voltage, when the lithium ion secondary batteryis charged.
 11. The lithium ion secondary battery system as set forth inclaim 8, further comprising a detection unit which detects the dischargerate of the lithium ion secondary battery, wherein said control unitcarries out said intermittent power feeding when the discharge rate ofthe lithium ion secondary battery is not less than 5 C.
 12. The lithiumion secondary battery system as set forth in claim 8, wherein thelithium ion secondary battery includes a positive active material havingan average discharge potential to the lithium metal of not less than4.5V.
 13. The lithium ion secondary battery as set forth in claim 8,wherein the lithium ion secondary battery is incorporated in a powersupply device of an electric automobile or a hybrid automobile.
 14. Thelithium ion secondary battery system as set forth in claim 8, furthercomprising a detection unit which detects the charge rate of the lithiumion secondary battery, wherein said control unit carries out anintermittent power feeding in which a power feeding and a pause arerepeatedly executed, when a lithium ion secondary battery is chargedwith not less than a predetermined charge rate.
 15. The lithium ionsecondary battery system as set forth in claim 14, further comprising adetection unit which detects the charge rate of the lithium ionsecondary battery, wherein said control unit carries out saidintermittent power feeding when the charge rate of the lithium ionsecondary battery is not less than 5 C.
 16. A method of operating alithium ion secondary battery system comprising: intermittentlysupplying power from the battery by repeatedly alternating a period ofsupplying power and a period of pausing the supplying of power when thebattery is discharged at a rate equal to or greater than a predetermineddischarge rate to a discharge end voltage, wherein the period of pausingthe supplying of power is equal to or greater than the period requiredfor the battery voltage to restore to at least 70% of an open circuitbattery voltage after the lithium ion secondary battery is dischargeduntil the voltage thereof reaches the discharge end voltage, when thelithium ion secondary battery is discharged.
 17. The method as set forthin claim 16, wherein power is intermittently supplied to the battery byrepeatedly alternating a period of supplying power and a period ofpausing the supplying of power when the battery is charged at a rateequal to or greater than a predetermined charge rate, wherein the periodof pausing the supplying of power is equal to or greater than the periodrequired for the battery voltage to go down by at least 70% of a voltagedifference between the open circuit voltage of the battery and a chargeend voltage of the battery.
 18. The method as set forth in claim 16,wherein the predetermined discharge rate is equal to or greater thanfive time the nominal capacity of the battery.